The present invention is directed to a variable speed induced draft fan and motor for a gas furnace.
Induced draft blowers remove the corrosive waste gases remaining after combustion occurs within the heat exchange cells of a furnace. The induced draft blower induces a draft within the heat exchanger cell and then impels the gases through the blower and into a chimney, a vent or the like.
A constant speed draft inducer blower is susceptible to operational changes due to transient conditions. As an example, furnaces that are vented from the induced draft blower in a horizontal direction are susceptible to gusts of wind that blow into the vent pipe and cause a pressure change. This pressure change is sensed by a pressure switch which opens and shuts down the furnace.
Additionally, constant speed induced draft blowers are affected by the environment in which they are located. The length and diameter of the vent or chimney should be within desired ranges in order for a constant speed induced draft blower to operate properly. Additionally, the constant speed induced draft blower cannot compensate for changes or blockages in the vent or chimney.
Also, a constant speed induced draft blower cannot compensate for the environment in which it is installed. Installations at higher altitudes require a costly and time consuming high altitude retrofit kit.
It is an object, feature and advantage of the present invention to provide an induced draft blower for a gas furnace which solves the problems with the prior art blowers.
It is an object, feature and advantage of the present invention to provide an induced draft blower which operates using a variable motor speed.
It is an object, feature and advantage of the present invention to provide a variable speed induced draft blower motor for a gas furnace which learns its proper operating point.
It is a further object, feature and advantage of the present invention that the induced draft blower learn its proper operating point without sensing airflow.
It is a further object, feature and advantage of the present invention that the induced draft blower motor learn its proper operating point using a high pressure and a low pressure switch.
It is an object, feature and advantage of the present invention to facilitate communication between the induced draft blower and an integrated furnace controller.
It is a further object, feature and advantage of the present invention to facilitate this communication using a minimum number of signals and wiring connections between the integrated controller and the inducer motor.
It is an object, feature and advantage of the present invention to provide a variable speed draft inducer that allows the furnace to maintain proper fuel/air mixture by speeding up or slowing down to maintain a proper air flow through the heat exchangers.
It is an object, feature and advantage of the present invention to provide a furnace with longer vent pipes than have previously been practical using typical induction motor draft inducers.
It is a further object, feature and advantage of the present invention to operate with the optimum fuel/air mixture over the entire operating range without regard to vent pipe lengths.
It is a further object, feature and advantage of the present invention to operate at a slower speed with short vent pipe lengths while providing quieter operation and maintaining proper combustion airflow.
It is an object, feature and advantage of the present invention to provide a variable speed inducer which allows the furnace to continue to operate safely through transient conditions that shutdown typical induce draft furnaces.
It is a further object, feature and advantage of the present invention to provide a variable speed inducer that responds to pressure changes by speeding up to maintain the correct airflow through the heat exchanger.
It is an object, feature and advantage of the present invention to provide a variable speed inducer which adapts to the installation regardless of the length of vent pipe installed.
It is an object, feature and advantage of the present invention to provide a variable speed inducer which compensates for the altitude of the installation without the necessity of costly and time consuming high altitude retrofit kits.
The present invention provides a method of controlling a variable speed draft inducer motor and fan in a gas furnace. The method comprises the steps of: detecting a first fault driving the motor to a maximum operating range; detecting a second fault forcing the motor to operate towards a minimum operating range; and generating a fault signal if both faults are detected substantially simultaneously.
The present invention also provides a method of controlling a variable speed draft inducer motor and fan in a gas furnace. The method comprises the steps of: determining if a motor is in a start-up condition; measuring the temperature of ambient air; determining if the measured air temperature is less than a cold temperature threshold; and enhancing the performance of the inducer fan motor if the measured ambient air temperature is less than the cold temperature threshold.
The present invention further provides a method of ensuring proper operation of a motor. The method comprises the steps of: detecting a first fault driving the motor to a maximum operating range; detecting a second fault forcing the motor to operate towards a minimum operating range; and generating a fault signal if both faults are detected substantially simultaneously.
The present invention yet further provides a method of protecting the operation of a motor operatively coupled to and motivating a fan. The method comprises the steps of: operating the motor at a desired motor speed; sensing the motor torque at the desired speed; determining, responsive to the sensed torque, whether the motor is operating at a first unfired condition; determining, responsive to the sensed torque, whether the motor is operating at a second fired condition; maintaining a first fan pressure drop if the motor is operating in the unfired condition; and maintaining a second fan pressure drop if the motor is operating in the fired condition; sensing the fan pressure drop.
The present invention still further provides a method of operating an inducer motor. The method comprises the steps of: determining if the inducer motor is in a start-up condition; measuring the temperature of ambient air; determining if the measured air is less than a cold temperature threshold; and enhancing the performance of the inducer fan if the measured ambient air is less than the cold temperature threshold.